1. Field of the Invention
This invention relates to a method for increasing the total amount of lattice metal in the framework of a particular porous inorganic crystalline composition comprising 98 mole percent or more SiO.sub.2 and 2 mole percent or less oxides of at least one initial lattice metal selected from those of Groups IIIB, IVB, VB, VIB, VIIB, VIII, IIIA, IVA and VA of the Periodic Table of the Elements, which comprises contacting the crystalline composition with a particular volatile compound comprising at least one metal to be coordinated in the framework of said crystalline composition, whereby the total amount of lattice metal subsequent to the contacting is greater than the amount of the initial lattice metal prior to the contacting. The volatile compound for use herein comprising the metal for lattice incorporation must have a radius ratio of less than about 0.6 and a size and shape which would permit it to enter the pores of the crystalline composition at the contacting temperature.
The volatile compound contacted inorganic crystalline composition may then be converted to the hydrogen or hydronium form and used as a catalyst component for conversion of organic compounds.
2. Description of Prior Art
High silica-containing zeolites are well known in the art and it is generally accepted that the ion exchange capacity of the crystalline aluminosilicate is directly dependent on its aluminum content. Thus, for example, the more aluminum there is in a crystalline structure, the more cations are required to balance the electronegativity thereof, and when such cations are of the acidic type such as hydrogen, they impart tremendous catalytic activity to the crystalline material. On the other hand, high silica-containing zeolites having little or substantially no aluminum, have many important properties and characteristics and a high degree of structural stability such that they have become candidates for use in various processes including catalytic processes. Materials of this type are known in the art and include high silica-containing aluminosilicates such as ZSM-5 (U.S. Pat. No. 3,702,886), ZSM-11 (U.S. Pat. No. 3,709,979), and zeolite ZSM-12 (U.S. Pat. No. 3,832,449) to mention a few.
The silica-to-alumina mole ratio of a given zeolite is often variable; for example, zeolite X can be synthesized with a silica-to-alumina ratio of from 2 to 3; zeolite Y from 3 to about 6. In some zeolites, the upper limit of silica-to-alumina mole ratio is virtually unbounded. Zeolite ZSM-5 is one such material wherein the silica-to-alumina ratio is at least 5. U.S. Pat. No. 3,941,871 discloses a crystalline metal organosilicate essentially free of aluminum and exhibiting an X-ray diffraction pattern characteristic of ZSM-5 type aluminosilicate. U.S. Pat. Nos. 4,061,724; 4,073,865 and 4,104,294 describe microporous crystalline silicas or silicates wherein the aluminum content present is at impurity levels.
Because of the extremely low aluminum content of these high silica-containing zeolites, their ion exchange capacity is not as great as materials with a higher aluminum content. For instance, the crystalline compositions to be treated hereby will have ion exchange capacity of less than about 0.7 meq/gram, whereas zeolite Y will exhibit an ion exchange capacity of from about 4.32 to about 7.1 meq/gram. Therefore, when the high silica materials are contacted with an acidic solution and thereafter are processed in a conventional manner, they are not as catalytically active as their higher aluminum-containing counterparts.
The novel method of this invention permits the preparation of certain high silica-containing materials which have all the desirable properties inherently possessed by such high silica materials and, yet, have a catalytic activity which heretofore has only been possible to be achieved by materials having a higher aluminum content in their "as synthesized" form.
It is noted that U.S. Pat. Nos. 3,354,078 and 3,644,220 relate to treating certain crystalline aluminosilicates with volatile metal halides. Neither of these latter patents are, however, concerned with treatment of crystalline materials having a high silica/alumina mole ratio and exhibiting a low cation exchange capacity of less than about 0.7 meq/gram. In fact, the methods of these latter patents are critically dependent on the presence of exchangeable cations or exchange capacity in the crystalline aluminosilicate. Also, the latter patents relate to ion exchange of the aluminosilicates having exchangeable cations. The present method relies, instead, upon incorporation of certain elements into a framework.